The present invention relates to a fluid operated wrench for tightening or loosening threaded connectors.
Fluid operated wrenches of the above mentioned general type are known in the art. One of such wrenches is disclosed in my U.S. Pat. Nos. 4,368,655 and 4,409,865. This hydraulic wrench has a support, a ratchet gear mounted turnably on the support, and a pair of driving pawls which have free ends engaging the teeth of the ratchet gear and are driven from a reciprocable driving element along a forward and a rearward stroke via a transmission. The transmission between the driving element and the drive pawls are constructed and arranged so that during the forward stroke of the driving element one of the driving pawls is moved in a given direction along an active stroke driving the ratchet gear through a given angle and the other of the driving pawls is moved along a return stroke to move in a direction opposite to the given direction over at least one tooth of the ratchet gear, whereas during the rearward stroke of the driving element the other driving pawl is moved along its active stroke and the one driving pawl is moved along its return stroke. When the fluid operated wrench is designed as described herein above, it has a continuous ratchet drive, with which the ratchet gear is turned through predetermined angles during the forward stroke as well as during the return stroke of the driving element.
The disadvantage of this wrench is that the pawls rub against the teeth of the ratchet gear during their active stroke. When the high power is applied this causes early fatigue of the material and breakage of the teeth of the ratchet gear. In addition, the driving pawls change their leverage during their active stroke and therefore cause inaccuracies in excess of the acceptable 5%, which is important for the accuracy of the applied torque. This change in leverage is caused by the movement of the pawls in the tooth of the ratchet gear, which results from the fact that the pawls swing during their active stroke in a direction which deviates from the direction normal to the circumference of the ratchet gear.
It is also known that all high powered fluid operated wrenches have a complicated construction with either a pivotally attached cylinder or a pivotally attached piston rod of the cylinder-piston drive unit. This is necessary because otherwise movements of the lever arm along a path which is curved around its pivot axis and movements of the piston rod along a straight path would cause the rod to bend and to ruin the piston seal. It is also known that wrenches as described above are single-purpose wrenches, usually for limited clearance applications where the reaction point is on the same plane as the tool housing.